The present invention relates to fluid level controllers and, more particularly, to such a controller for use in a container that cryogenically cools an electronic device.
Certain electronic devices, such as CMOS (complementary-metal-oxide semiconductor) integrated circuit (IC) chips, have been found to operate at significantly greater speeds when cooled to very low temperatures, for example -140.degree. F. The use of cryogenic methods for cooling electronic devices has thus been proposed for (and in some cases commercially used in) computer systems.
In a typical cryogenic system for cooling an electronic device, the device is placed in a container having a cryogenic fluid, such as liquid nitrogen. Heat from the electronic device is absorbed by the fluid, and resulting vapors are vented from the container. It therefore become necessary to frequently replenish the cryogenic fluid in the container. As part of the replenishment, there must be provided a mechanism to control the level of fluid in the container in order to assure that a proper amount of cryogenic fluid will be available at all times to cool the electronic device.
Fluid level controllers are known in the art, but they are not well suited for the type of cryogenic containers used for cooling electronic devices. For example, a cryogenic container holding an electronic device usually has rather small dimensions, requiring that the level controller likewise be small. Prior level controllers for containers having cryogenic fluids have tended to be large (sometimes even mounted outside of the container) since they are designed for large tanks rather the the small container that would typically be found in a computer system.
Some prior controllers operate from the pressure within the container. For example, a sensor tube may extend into the container and the controller senses a change in pressure in the tube when the tube is closed as a result of the fluid rising from a level below the opening of the tube to a level above the opening of the tube. The problem with such a controller is that the pumping of the cryogenic fluid into the container from a supply tank often requires that the supply tank be at a significantly greater pressure than the container. Requiring also that the container have a sufficiently high pressure in order to use a sensor tube to control its fluid level (since the space above the fluid needs to be at a relatively high pressure in order to be sensed by the sensor tube) increases the amount of pressure needed to pump the fluid from the supply tank into the container and adds to the complexity and cost of the system.
There has thus arisen the need for a fluid level controller that occupies minimal space, that can be placed in a container containing cryogenic fluid for cooling an electronic device, and that is simple in design and inexpensive to manufacture.